CiiAP. VI. OF NATURAL SELECTION. 189 



the passage of a litely-cxpandcd flower, and arc thus carried 

 away. Dr. Cril<^('r sent ine a (lower in spirits of wine, with a 

 bee which he liad killed before it liad ([uite crawled ont with a 

 pollen-mass still fastened to its back. When the bee, thus 

 provided, (lies to another (lower, or to the same flower a sec- 

 ond time, and is jnished by its comrades into the bucket and 

 then crawls out by the iiassag-e, the pollen-mass necessarily 

 comes first into contact with the viscid stig'ma, and adheres to 

 it, and the (lower is fertilized. Now at last we see the full 

 use of every part of the flower, of the water-secreting horns, 

 of the bucket half full of water, wliicli prevents the bees from 

 flving away and forces them to crawl out through the spout, 

 and lub against the properly-placed viscid pollen-masses and 

 viscid stigma. 



The construction of tlie (lower in another closely-allied or- 

 chid, namely, the Catasetum, is widely dilVerent, though serving 

 the same end; and is equally curious. Bees visit these flow- 

 ers, like those of the Coryanthes, in order to gnaw the label- 

 lum ; in doing this they inevitably touch a long, tapering, 

 sensitive projection, or, as I have called it, the antenna. This 

 antenna, when touched, transmits a sensation or vibration to a 

 certain membrane which is instantly ruptured ; this sets free 

 a spring by which the pollen-mass is shot forth, like an arrow, 

 in the right direction, and adheres by its viscid extremity'' to 

 the back of the bee. The pollen-mass of a male plant is thus 

 carried to the flower of a female plant, where it is brought into 

 contact with the stigma, which is A'iscid enough to break cer- 

 tain elastic threads, and, retaining the pollen, fertilization is 

 elTected. 



How, it may be asked, in the foregoing and in innumerable 

 other instances, can we imderstand the graduated scale of 

 complexity and the multifarious means for gaining the same 

 end V The answer no doubt is, as already remarked, that when 

 two forms vary, which already diller from each other even in a 

 slight degree, tht; variability will not be of the same exact na- 

 ture, and conseciuently the results obtained through natural 

 selection for the same general ])urpose will not be the same. 

 We should also bear in mind that every highly-developed or- 

 ganism has passed through a long course of modilication; and 

 that each moditied structure tends to be inherited, so that it 

 will not readily be wholly lost, but may be modified again and 

 again. Hence the structure of each part of each species, for 

 whatever purpose used, is the sum of the many inherited 



